Vokera 20/80 RS Flowmatic DHW Expansion Vessel Pressure

[Robbie1980]

I have a Vokera 20/80 RS Flowmatic boiler and the system pressure has risen up towards 3 bar when hot and when cold always ends on a higher pressure that it was set to.

For example, i'd set the system cold to 1bar and then few days later after the heating has been on it will rest at 1.4/1.5bar.

Have checked the main expansion vessel (though difficult to do due to space constraints!)and is just under 1barg (manual says 1barg) but the DHW expansion vessel has no pressure!

I've looked in all my manuals and guides and a pressure isn't specified for the DHW expansion vessel, only the main one. Should they be the same?

If so, i think i shut the external cold supply to the boiler and then run the kitchen tap to relieve the back pressure before re-pressurising the DHW vessel?

Any help would be appreciated,
Rob

 

[twgas]

dhw exp ves wouldnt affect system pressure, more likely to be filling loop passing or dhw heat exchanger pinholed

 

[weareleeds]

Another possibility is the stuffing box washer is leaking which allows mains water to pass into htg circuit through 3 port valve (very common)

 

[Robbie1980]

Another possibility is the stuffing box washer is leaking which allows mains water to pass into htg circuit through 3 port valve (very common)

cheers for the advice. Have had a look at the manual/instructions and am struggling to locate this washer.

Does the stuffing box washer have a different name?
thank
Rob

 

[DP]

It is known as the 'tail piece'. Fits between the diverter and the domestic manifold. Another item that may be the culprit is the O ring on domestic manifold cover.

In fact a service should cure all ills on this boiler. One of the few boilers that does not suffer from intermittent faults.

 

[Robbie1980]

Gents,

Still having the rising system pressure problem on my vokera 80-20.

It's def not the filling loop and CH expansion vessel is at the correct pressure 1barg.

Had the heating on the other day (for a while) and went to check the pressure and was about 3.2bar. Why hasn't the safety valve blown off the pressure? This makes me think is the display pressure actually correct?
Is there a way of venting the pressure needle display pipe?

People have mentioned various washers which could be passing and pressurising the system and vokera have also said it could be a fractured heat exchanger. I know i need some help on this so can someone give me an idea of an estimated prices to rectifiy this problem?

I don't mind paying to sort the problem but don't want to have to keep changing different things and paying time and labour several times which could well rack up to a lot of money.

Advice welcome,
Thanks,
Rob

 

[ChrisR]

It's an old boiler. Even from here I can tell it has a lot of things which aren't working like the designer intended!

Unless you can find an expert, I'd say call Vokera, though I recently heard they refused to work on one because they said they couldn't get the nuts on the secondary heat exchanger undone, which is laughable.
There will be some scale/sludge, which they might say someone else has to deal with.

Everyone wants a quick, good and cheap solution - they become difficult!

 

[Robbie1980]

It's an old boiler. Even from here I can tell it has a lot of things which aren't working like the designer intended!

Unless you can find an expert, I'd say call Vokera, though I recently heard they refused to work on one because they said they couldn't get the nuts on the secondary heat exchanger undone, which is laughable.
There will be some scale/sludge, which they might say someone else has to deal with.

Everyone wants a quick, good and cheap solution - they become difficult!

thanks for the reply Chris,

It's not that i'm after a cheap solution - naturally everyone wants this to any problem!

I have tried the obvious things (for me) and it's not them. I know i need help from an engineer hence my questions regarding price. From your response i assume you think a new boiler would be advisable?

If so, can a new condensing combi boiled fit as a direct replacement? if so, can anyone recommend any makes and models and places to get them.
Cheers,
Rob

 

[ChrisR]

Sorry no I wasn't meaning to be so glib.
I mean - you might fnd a boiler man who knows these really well and say, sorts O ring problems in one callout, costing little, then you try it and see, but then you have more problems...
Or you could take it to bits yourself, costing less but taking longer, or you could of course change the boiler, which may cost £2000 and open another can of worms.

You have to decide which of the three desirables is more important!

 

[DP]

How did you check the expansion vessel pressure. What I mean is, what pressure was indicated on the pressure vessel when you checked the pressure on the expansion vessel?

 

[Robbie1980]

How did you check the expansion vessel pressure. What I mean is, what pressure was indicated on the pressure vessel when you checked the pressure on the expansion vessel?

Hi,

I checked the expansion vessel pressure with a car tyre (schrader valve) indicater. It was 1barg.

I think i checked it when the heating had been off for a while so the system pressure (cold) would have been between 1 and 1.5bar.

I see what you are saying. The 1 barg quoted by vokera in the manual for the expansion CH vessel - is that 1bar when (isolated) and when part of a system with the cold water pressure should infact be 1bar + cold water pressure? If so, i may have been measuring system water pressure and the inert gas? in the expansion vessel may well have dissipated?

I guess i can check this by draining system to 0.5bar and seeing if the expasnsion vessel pressure drops to 0.5bar too?

Looking forward to your response.
Thanks
Rob

 

[twgas]

I believe you are thinking correctly. you need to open a drain-off (and leave it open) to check and adjust the pressure in the vessel.

 

[Robbie1980]

I will try that tomorrow night hopefully.

Say i have set my cold water pressure at 1bar and dont use the central heating - am i right in thinking that using hot water should not cause any increase in system pressure as the heating is an isolated circuit with the expansion vessel as part of that circuit.

Hence if the system pressure continues to rise, water is passing into the heating circuit (as mentioned in previous posts via an o ring seal or pin holed DHW expansion vessel)


Cheers

 

[Robbie1980]

I set the cold water pressure at 1.35bar yesterday evening and this morning was just under 1.5bar

Have not used the heating only hot water. Could this still be explained by an incorrectly pressurised expansion vessel (CH)? Obviously i don't want to drain the system if not.

If i do drain the system what's the best way? I usually open a radiator but takes ages. Don't want to use the safety valve blow off as apparently doesnt always seat properly and can leak when used.

Will shutting the stop cock and running cold water drain the water already in the boiled heat exchanger?

Thanks again,

Rob

 

[twgas]

to drain system you need a drain cock

using hot water will increase system pressure to some degree. try turning boiler off before you go to work and then check pressure when you get home.

shutting water off and opening tap will drain (or at least release the pressure) the domestic side of the secondary h/ex[/img]